Langmuir monolayers technique

Planar polymer films were recently mineralized with calcium phosphate [267], Using the Langmuir monolayer technique, it was possible to control the particle growth by the polymer film properties at the air-water interface and the subphase parameters (pH, ion strength). Small changes it the growth conditions resulted in various particle shapes and dimensions. Such examples of controlled biomimetic mineralization are indeed very motivating for further studies of crystallization processes in synthetic membranes. 

In order to determine the infants lung maturity and the necessity of surfactant therapy it is of great importance to substantiate the functionality of the alveolar surfactant, derived via invasive techniques [13], Several techniques and models have been largely used to investigate inteifacial physicochemical properties in vitro and to assess clinical efficiency of ES in vivo the Langmuir monolayer technique in combination with Wilhelmy plate method for surface tension measurements and black foam film method for determination of the ability of ES for stable film formation [14]. The pendant drop method combined with the Axisym-metric Drop Shape Analysis (ADSA) has been also used for similar purposes [4,15-18]. 

Meldrum, F. C., N. A. Kotov, and J. H. Fendler. 1995. Formation of thin-films of platinum, palladium, and mixed platinum/paUadiun nanocrystalhtes by the Langmuir monolayer technique. Chem. Mater. 7(6) 1112-1116. 

Since the first systematic study of monolayers of amphiphilic molecules at the air-water interface published by Langmuir in 1917 [1], Langmuir monolayers have served mainly as model systems to mimic biological membranes. With the development of nanotechnology in the last two decades, the Langmuir monolayer technique has become an efficient tool to make nanoscale materials, especially as thin films for chemical and biosensor development [2-5]. 

In the case of Langmuir monolayers, film thickness and index of refraction have not been given much attention. While several groups have measured A versus a, [143-145], calculations by Knoll and co-workers [146] call into question the ability of ellipsometry to unambiguously determine thickness and refractive index of a Langmuir monolayer. A small error in the chosen index of refraction produces a large error in thickness. A new microscopic imaging technique described in section IV-3E uses ellipsometric contrast but does not require absolute determination of thickness and refractive index. Ellipsometry is routinely used to successfully characterize thin films on solid supports as described in Sections X-7, XI-2, and XV-7. 

The external reflection of infrared radiation can be used to characterize the thickness and orientation of adsorbates on metal surfaces. Buontempo and Rice [153-155] have recently extended this technique to molecules at dielectric surfaces, including Langmuir monolayers at the air-water interface. Analysis of the dichroic ratio, the ratio of reflectivity parallel to the plane of incidence (p-polarization) to that perpendicular to it (.r-polarization) allows evaluation of the molecular orientation in terms of a tilt angle and rotation around the backbone [153]. An example of the p-polarized reflection spectrum for stearyl alcohol is shown in Fig. IV-13. Unfortunately, quantitative analysis of the experimental measurements of the antisymmetric CH2 stretch for heneicosanol [153,155] stearly alcohol [154] and tetracosanoic [156] monolayers is made difflcult by the scatter in the IR peak heights. 

Sotobayashi FI, Schilling T and Tesche B 1990 Scanning tunnelling microscopy of polyimide monolayers prepared by the Langmuir-Blodgett technique Langmuir 6 1246... 

Dominguez, D.D.,Mowery, R. L., and Turner, N. H., Friction and Durabilities of Well-Ordered, Close Packed Carboxylic Acid Monolayers Deposited on Glass and Steel Surfaces by the Langmuir-Blodgett Technique, Tribal. Trans., yi. No. 1, 1994, pp. 59-66. 

The other method of monolayer transfer from the air/water interface onto solid substrates is illustrated in Figure 2. This method is called the Langmuir-Schaefer technique, or horizontal lift. It was developed in 1938 by I. Langmuir and V. Schaefer for deposition of protein layers. Prepared substrate horizontally touches the monolayer, and the layer transfers itself onto the substrate surface. The method is often used for the deposition of rigid monolayers and for protein monolayers, hi both cases the apphcation of the Lang-muir-Blodgett method produces defective films. 

Modified electrodes containing cyclam derivatives have been prepared. The approach utilizing cyclam incorporated in Nafion film on a carbon electrode shows that the catalytic efficiency of the system is much lower than observed when the catalyst is adsorbed on the mercury. With electrodes prepared following the Langmuir Blodgett technique, only the electrode materials that allow the orientation of the monolayer so that the tail points to the substrate were found to be electrocatalytically active.165... 

Fig. 3.5 Representation of a scheme of an experiment (upper set of drawings) and the obtained experimental results presented as AFM images (middle part) and cross-sectional profiles (bottom) that provides evidence of silica nucleation and shell formation on biopolymer macromolecules. Scheme of experiment. This includes the following main steps. 1. Protection of the mica surface against silica precipitation. It was covered with a fatty (ara-chidic) acid monolayer transferred from a water substrate with the Langmuir-Blodgett technique. This made the mica surface hydrophobic because of the orientation of the acid molecules with their hydrocarbon chains pointing outwards. 2. Adsorption of carbohydrate macromolecules. Hydrophobically modified cationic hydroxyethylcellulose was adsorbed from an aqueous solution. Hydrocarbon chains of polysaccharide served as anchors to fix the biomacromolecules firmly onto the acid monolayer. 3. Surface treatment by silica precursor. The mica covered with an acid mono-...

Three versions of this concept have been used to prepare LB film containing MCs. In the first, pioneered by Fendler (13-16), a compressed Langmuir monolayer is used as a template for the preparation of Q-state particles. For instance, diffusion of H2S through a monolayer of dodecylbenzenesulfonic acid (17) or a bis amine type surfactant (14) into a Cdz+ solution resulted in the growth of Q-state CdS under the monolayer. The vertical dipping technique (Fig. 3.5.2) was then used to transfer the monolayer, with associated semiconductor, to a substrate to give multilayer LB films. 

FIG. 7.1 Deposition of multilayers using the Langmuir-Blodgett technique (a and b) monolayer deposition and (c and d) multilayer deposition. 

We have studied the photoelectrochemical behavior of Chi a and Chi b on an n-type Sn02 (60) optically transparent electrode (OTE thickness of the Sn02 layer on the glass substrate, ca. 2000 A donor density, 1020-21cm-3). Chi monolayer assemblies, deposited by means of the Langmuir-Blodgett technique (20,21), were employed. The use of such monolayer assemblies as interfacial dye layers... 

Monolayers can be transferred onto solid substrates by the Langmuir-Blodgett technique giving rise to mono- or multilayers which can even have thicknesses in the range of the wavelength of visible light. The multilayer quality often depends on the quality of the first monolayer transfer. 

Monolayer Films of Phthalocyanine Derivatives. A series of organic derivatives of phthalocyanines were prepared that have two important characteristics of materials to be deposited by the Langmuir-Blodgett technique (1) they are soluble in volatile organic solvents, and (2) they form monomolecular films on the surface of water. Further study of deposited films of these phthalocyanine derivatives will be necessary in order to determine the exact orientations on the surface, but regardless of their orientations, they offer interesting possibilities for construction of thin films of ordered arrays of molecules on the surface of gas sensors. 

Figure 13.4 Transfer of a monolayer from an aqueous surface to a solid substrate via the Langmuir-Blodgett technique.

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